This paper presents an experimental study of the factors modulating the urgency perception of voice alarm generated by concatenative synthesizers. Four experiments were conducted using psycho-physical approach in which 105 participants made magnitude estimation for urgency perception of various voice alarm stimuli. Experiment 1 identified 6 acoustic and non-acoustic factors modulating the perceived urgency of synthesized voice alarm. Experiment 2, 3 and 4 quantified the relations between the objective changes in each of the quantifiable parameters and the subjective changes in urgency perception. This research has implications for the design and implementation of synthesized voice alarm systems where urgency mapping is required.